Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userWide-Band Spectra of Giant Radio Pulses from the Crab Pulsar
74
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present the results of the simultaneous observation of the giant radio pulses (GRPs) from the Crab pulsar at 0.3, 1.6, 2.2, 6.7, and 8.4 GHz with four telescopes in Japan. We obtain 3194 and 272 GRPs occurring at the main pulse and the interpulse phases, respectively. A few GRPs detected at both 0.3 and 8.4 GHz are the most wide-band samples ever reported. In the frequency range from 0.3 to 2.2 GHz, we find that about 70% or more of the GRP spectra are consistent with single power laws and the spectral indices of them are distributed from $-4$ to $-1$. We also find that a significant number of GRPs have such a hard spectral index (approximately $-1$) that the fluence at 0.3 GHz is below the detection limit (dim-hard GRPs). Stacking light curves of such dim-hard GRPs at 0.3 GHz, we detect consistent enhancement compared to the off-GRP light curve. Our samples show apparent correlations between the fluences and the spectral hardness, which indicates that more energetic GRPs tend to show softer spectra. Our comprehensive studies on the GRP spectra are useful materials to verify the GRP model of fast radio bursts in future observations.
rate research
Read More
Individual giant radio pulses (GRPs) from the Crab pulsar last only a few microseconds. However, during that time they rank among the brightest objects in the radio sky reaching peak flux densities of up to 1500 Jy even at high radio frequencies. Our observations show that GRPs can be found in all phases of ordinary radio emission including the two high frequency components (HFCs) visible only between 5 and 9 GHz (Moffett & Hankins, 1996). This leads us to believe that there is no difference in the emission mechanism of the main pulse (MP), inter pulse (IP) and HFCs. High resolution dynamic spectra from our recent observations of giant pulses with the Effelsberg telescope at a center frequency of 8.35 GHz show distinct spectral maxima within our observational bandwidth of 500 MHz for individual pulses. Their narrow band components appear to be brighter at higher frequencies (8.6 GHz) than at lower ones (8.1 GHz). Moreover, there is an evidence for spectral evolution within and between those structures. High frequency features occur earlier than low frequency ones. Strong plasma turbulence might be a feasible mechanism for the creation of the high energy densities of ~6.7 x 10^4 erg cm^-3 and brightness temperatures of 10^31 K.
To search for giant X-ray pulses correlated with the giant radio pulses (GRPs) from the Crab pulsar, we performed a simultaneous observation of the Crab pulsar with the X-ray satellite Hitomi in the 2 -- 300 keV band and the Kashima NICT radio observatory in the 1.4 -- 1.7 GHz band with a net exposure of about 2 ks on 25 March 2016, just before the loss of the Hitomi mission.The timing performance of the Hitomi instruments was confirmed to meet the timing requirement and about 1,000 and 100 GRPs were simultaneously observed at the main and inter-pulse phases, respectively, and we found no apparent correlation between the giant radio pulses and the X-ray emission in either the main or inter-pulse phases.All variations are within the 2 sigma fluctuations of the X-ray fluxes at the pulse peaks, and the 3 sigma upper limits of variations of main- or inter- pulse GRPs are 22% or 80% of the peak flux in a 0.20 phase width, respectively, in the 2 -- 300 keV band.The values become 25% or 110% for main or inter-pulse GRPs, respectively, when the phase width is restricted into the 0.03 phase.Among the upper limits from the Hitomi satellite, those in the 4.5-10 keV and the 70-300 keV are obtained for the first time, and those in other bands are consistent with previous reports.Numerically, the upper limits of main- and inter-pulse GRPs in the 0.20 phase width are about (2.4 and 9.3) $times 10^{-11}$ erg cm$^{-2}$, respectively. No significant variability in pulse profiles implies that the GRPs originated from a local place within the magnetosphere and the number of photon-emitting particles temporally increases.However, the results do not statistically rule out variations correlated with the GRPs, because the possible X-ray enhancement may appear due to a $>0.02$% brightening of the pulse-peak flux under such conditions.
Giant radio pulses (GRPs) are sporadic bursts emitted by some pulsars, lasting a few microseconds. GRPs are hundreds to thousands of times brighter than regular pulses from these sources. The only GRP-associated emission outside radio wavelengths is from the Crab Pulsar, where optical emission is enhanced by a few percent during GRPs. We observed the Crab Pulsar simultaneously at X-ray and radio wavelengths, finding enhancement of the X-ray emission by $3.8pm0.7%$ (a 5.4$sigma$ detection) coinciding with GRPs. This implies that the total emitted energy from GRPs is tens to hundreds of times higher than previously known. We discuss the implications for the pulsar emission mechanism and extragalactic fast radio bursts.
The results of simultaneous multifrequency observations of giant radio pulses from the Crab pulsar, PSR B0531+21, at 23, 111, and 600 MHz are presented and analyzed. Giant pulses were detected at a frequency as low as 23 MHz for the first time. Of the 45 giant pulses detected at 23 MHz, 12 were identified with counterparts observed simultaneously at 600 MHz. Of the 128 giant pulses detected at 111 MHz, 21 were identified with counterparts observed simultaneously at 600 MHz. The spectral indices for the power-law frequency dependence of the giant-pulse energies are from -3.1 to -1.6. The mean spectral index is -2.7 +/- 0.1 and is the same for both frequency combinations (600-111 MHz and 600-23 MHz). The large scatter in the spectral indices of the individual pulses and the large number of unidentified giant pulses suggest that the spectra of the individual giant pulses do not actually follow a simple power law. The observed shapes of the giant pulses at all three frequencies are determined by scattering on interstellar plasma irregularities. The scatter broadening of the pulses and its frequency dependence were determined as tau_sc=20*(f/100)^(-3.5 +/- 0.1) ms, where the frequency f is in MHz.
No apparent correlation was found between giant pulses (GPs) and X-ray photons from the Crab pulsar during 5.4 hours of simultaneous observations with the Green Bank Telescope at 1.5 GHz and Chandra X-Ray Observatory primarily in the energy range 1.5-4.5 keV. During the Crab pulsar periods with GPs the X-ray flux in radio emission phase windows does not change more than by +-10% for main pulse (MP) GPs and +-30% for interpulse (IP) GPs. During giant pulses themselves, the X-ray flux does not change more than by two times for MP GPs and 5 times for IP GPs. All limits quoted are compatible with 2-sigma fluctuations of the X-ray flux around the sets of false GPs with random arrival times. The results speak in favor of changes in plasma coherence as the origin of GPs. However, the results do not rule out variations in the rate of particle creation if the particles that emit coherent radio emission are mostly at the lowest Landau level.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
